Try to write immediately after reading

src/server.cpp

@@ -338,7 +338,10 @@ void Server::start_network_threads() {
             }
           }
 
-          if (events[i].events & EPOLLOUT) {
+          // Send immediately if we already already have outgoing messages from
+          // read callbacks.
+          if ((events[i].events & EPOLLOUT) ||
+              ((events[i].events & EPOLLIN) && conn->hasMessages())) {
             bool error = conn->writeBytes();
             if (error) {
               continue;